In operation of a scanner, light is emitted from a source to a object, then is reflected by a set of lens. Then, the light is focused on and received by a charge-couple device (CCD) or a complementary metal oxide semiconductor (CMOS). The light signal is transferred into electric signal by such light-sensing component, so that data of analog or digital pixels are produced. During the scanning, the intensity of the light reflected from different areas of the scanned object is detected by the CCD. The low density of light is reflected from a darker area of the scanned object and the high density of light is reflected from a lighter area of the scanned object. Since the reflected light is transferred into analog or digital data by the CCD, the electric signals are proportional to the light density. Then, the electric signals are transferred into a image file by an image software compatible for the scanner, a multi-function printer, a fax machine or a copy machine.
The performance of a scanner depends on the light-controlling technology, so that the quality of the optical module is very important for the performance of the scanner.
Presently, the contact image sensor is widely used in a scanner, wherein the contact image sensor is an assembly of a light source, a rod lens, a sensing substrate and a housing.
Please refer to FIG. 1(a) showing an optical module of a scanner having a contact image sensor (CIS) according to the prior art. The CIS module includes a diode source 11, a rod lens 12, a housing 13 and a circuit plate 14. A light-sensing component 141 constructed by CCD or CMOS is arranged on the circuit plate 14 as shown in FIG. 1(b).
During the operation of the optical module, the light reflected from the scanned object is focused on the light-sensing component 141 by the rod lens 12. If the distance between positions of the rod lens 12 centerline and the light-sensing component 141 centerline is significant, the scanning quality will be bad.
For the requirements of positioning light source, injection molding and mold release, the conventional design of the housing of an optical module is shown as FIGS. 2(a) and (b), which respectively show the top view and the side view of the assembly of the rod lens 12 and the housing 13 according to FIG. 1(a). Referring to FIG. 2(a), the rod lens 20 is arranged in a slot constructed by the first slot wall 22 and the second slot wall 23 of the housing 32, and the slot is filled with a fixing gel 25.
However, the second slot wall 23 is limited by an angle 221 formed between the second slot wall 23 and the vertical axis as shown in FIG. 2(b), and a torque is formed due to the difference between the heights of the fixing gel at two sides of the rod lens 20. Therefore, the rod lens 20 is inclined as shown in FIG. 2(c). The light reflected from the scanned object is focused by the rod lens 20 to form an image which is not on the predetermined position, and consequently the center of the image is not on the light-sensing component 24 arranged on the circuit plate 21 as shown in FIG. 2(d). The quality of the obtained image is bad owing to the rod lens effect or photo response non uniformity.
Therefore, the present invention provides a lens fixing structure and a method for fixing lens of an optical module in a scanner, a multi-function printer, a fax machine or a copy machine to overcome the disadvantages of the prior art described above.